Although lack of libido in men is often confused with impotence or erectile dysfunction, they are very different conditions. Men who suffer from low libido can often achieve erection but they have lost the desire to have sex, whereas men who suffer from impotence or erectile dysfunction want to have sex but can not achieve or maintain an erection long enough to do so.

Erectile dysfunction is relatively common and affects about one man in every ten, but on average, a GP will see one man suffering from lack of desire for every 15 suffering from erectile difficulties. Unlike erectile dysfunction, low sexual desire does not respond to Cialis, Levitra or Viagra and while Ed usually reflects an underlying medical condition, lack of libido can have a number of physical explanations.

You would be hard pressed not to notice the more obvious culprits — alcoholism, drug abuse, diabetes or obesity — but “not tonight, darling” can also be a side-effect of prescription medications, particularly those used in the treatment of prostate problems and, less frequently, it may relate to low levels of testosterone, an excess of the hormone prolactin or anaemia. If there is no physical explanation then the cause is more likely to be psychological. Depression, stress, financial problems, job insecurity, sexual hang-ups, confusion about sexual orientation, guilt about infidelity or just common or garden boredom can all lead to low sexual desire.

In their book He’s Just Not Up for It Anymore (HarperCollins) Bob Berkowitz and his wife Susan Yager-Berkowitz surveyed more than 4,000 men and women in sexless marriages across the US to try to understand this problem. In many cases male sexual performance was affected by illness, erectile dysfunction, side-effects of medications, or alcohol or drug dependency, and of course some men were simply in doubt about their marriage. Just 6 per cent of men blamed it on being “too tired”, and 9 per cent said that they didn’t have the time.

Boredom was the biggest issue; 68 per cent of men blamed their partner’s lack of sexual adventurousness, although as the authors rightly point out, the men failed to acknowledge that they made no novel contribution to their sexual relationships either.

Depressingly, 48 per cent said that they would enjoy sex with other women, just not their wives, and 25 per cent said they preferred to use internet porn for sex because it was less hassle. Many of them (44 per cent) were angry with their wives, feeling that they were constantly nagged and criticised. And 38 per cent said that their wives had gained a substantial amount of weight and they found them less attractive — their own weight was not a consideration.

The survey also revealed that 68 per cent of women did not know why their husbands had gone off sex and were bewildered and hurt by their partner’s indifference towards them. Some felt that sex was being withheld as a punishment and 57 per cent said they felt that their husbands were depressed.

Women are normally the emotional housekeepers in any relationship and they tend to be the ones who “demand” that issues are addressed but men are notoriously bad at confronting medical or psychological issues and so there is no resolution. Women who are married to men who have lost interest in sex and won’t do anything about it talk about the loneliness of living in a “sham” marriage which looks perfect from the outside but feels empty on the inside. Of course, their real anxiety is that their partner’s behaviour indicates a lack of interest in them and what they are really seeking is validation and reassurance, however every time a woman brings up the subject her partner is reminded that he is failing her in the bedroom.

Sometimes however, losing interest in sex is not a massive problem, particularly for aging couples who have developed other ways of remaining physically and emotionally affectionate. Difficulties only arise when one partner wants to remain sexually active and the other has lost interest and in these cases, resolution is only feasible if both parties are committed to finding a viable solution.